In hypertall buildings, it has been known to move passengers to the highest parts of the building by means of a series of elevators, the lower elevator taking the passengers to a first sky lobby, after which the passengers walk to another elevator for travel to a second sky lobby; thereafter, passengers may disperse in local elevators or travel in yet a third elevator to an additional sky lobby. The taller a building becomes, the more difficult it is to find sufficient space for elevators to move the requisite number of passengers to the higher ends of the building. Thus, it becomes more important with additional height that the use of the elevator core space be very efficient.
Another problem with hypertall buildings is that the weight of the elevator rope (the steel cables that support the car and the counterweight) preclude use of rope systems beyond about one hundred twenty floors, or so. Another problem with conventional elevators is that only one elevator can occupy an elevator hoistway at a time since it must be continuously roped to its counterweight, and since it reciprocates, up and down, in the hoistway.
It is suggested to overcome some of these problems by the use of elevators powered by linear electric motors (LEMs), which provide driving force to the elevator car directly from the building structure. However, without a counterweight, the size and power requirements for LEMs suitable to move elevator cars are at the present prohibitive for practical service.
In copending U.S. patent application Ser. No. 8/564,754, filed Nov. 29, 1995 now U.S. Pat. No. 5,657,835, an elevator cab travels in a car frame in one hoistway to a transfer floor where the car frame stops; the cab is moved to a car frame in an adjacent hoistway for further travel.